1. Field of the Invention
The invention relates to the field of composite structure fabrication, in particular, to an improved system for de-bulking the uncured composite sheets as they are laid up in a mold at the workstation.
2. Description of Related Art
Typically, composite structures are formed by a process that involves the following steps:    1. Sheets of filamentary material impregnated with uncured resin are laid up in a mold having the contour of the completed part.    2. After the lay-up is complete, the lay-up is vacuum bagged.    3. Thereafter a vacuum is pulled between the lay-up and mold.    4. The vacuum-bagged lay-up is then placed in an autoclave wherein the temperature is increased to the curing temperature of the resin and the autoclave is pressured until the resin is cured.    5. Thereafter, the cured lay-up and mold are removed from the oven or autoclave and the now cured part is removed from the mold.
However, often the number of plies in the lay-up requires multiple de-bulks during the lay-up process that a de-bulking procedure is required. Typically, the lay-up process requires a de-bulk after a certain number of plies of resin impregnated filamentary material have been laid up in the mold. The partially completed lay-up has to be vacuum bagged and a vacuum pulled in order to de-gas and consolidate it if this is not done, there is a high probability that the completed part will have unacceptable voids caused by air pockets. It is preferred that this de-bulking process take place at a temperature at which the resin will flow but not readily cure. Thus the mold with vacuum-bagged partially completed lay-up must be moved into the autoclave. If the part is vary large, thus requiring a large and heavy mold, the process and be difficult and time consuming.
Portable oven and autoclave type devices are available. For example, U.S. Pat. No. 5,116,216 “Apparatus For Preparing Thermoplastic Composites” by R. C. Cochran, et al. discloses an apparatus for fabricating composites using thermoplastic matrix materials. A blanket heater is placed over the lay-up is used to supply the necessary heating. An inner flexible vacuum bag is placed over the lay-up and sealed to the mold surface and a ridged outer chamber is placed over the flexible vacuum bag and also sealed to the mold surface. A differential vacuum is drawn from between the flexible vacuum bag and lay-up and between the vacuum bag and ridged outer chamber, with the higher vacuum drawn from under the flexible vacuum bag. The blanket heater is turned on and the lay-up heated until the thermoplastic material has melted. Thereafter, the lay-up is allowed to cool to ambient conditions. The problem with this apparatus is that, its advantage of portability is diminished if the part being formed is large. Secondly, if high compaction pressures were required, an autoclave would still be necessary, even if the apparatus was used for de-bulking. Further the heater system and rigid chamber is part specific and must be fabricated for each tool and lay-up.
Thus, it is a primary object of the invention to provide to provide a de-bulking system for the manufacture of composite parts that does not require the partially completed lay-up and mold to be placed in an autoclave.
It is another primary object of the invention to provide a de-bulking system for the manufacture of composite parts that is easily transportable.
It is a further object of the invention to provide a de-bulking system for the manufacture of composite parts that is inexpensive to manufacture and is can be easily adapted to various size parts.